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Topaz change color when heated


#1

This is such an obvious newby question that I hope you will all be
gentle!

I prematurely set a 12mm blue topaz cabochon into a sterling silver
bezel before realizing that I had not attached my bail to the
pendant, darn. Rather than remove the stone I pretended to protect
the front of the piece and the stone with Rio Extra Hands, carved
out a spot in my soldering block to rest the stone and pendant face
down and proceeded to solder the bail to the back of the pendant
using easy solder. As you can imagine disaster struck but not quite
in the way that I expected. The bail soldered on just fine but (of
course) the poor topaz cracked from the exposure to the heat and
completely lost all of its color. Now it looks like a rather nice
round piece of barely blue cracked crystal. It is the total color
change I am most interested in understanding. Will all stones change
color when subjected to heat? How much heat does it take? Is there a
way to protect a stone without removing it if you need to solder
something? Since everything is a lesson these days I don’t mind
losing the stone (too much) but would like to avoid repeating the
mistakes!

Thanks in advance for any advice.


#2

Hi Jane,

In general remember red, white, and blue can take heat… Diamond,
Sapphire, and Ruby…That’s it.

Nothing else can take heat. Especially in silver.

Although, come to think of it, the synthetic spinels…ie birth
stones…can usually take heat to a degree all except the green ones
which are doublets. Must air cool these though.

I have heard star sapphire and star ruby are heat sensitive too, so I
don’t suggest risking heating them.

Mark


#3

Hi Jane,

The blue topaz available are irradiated stones that can change color
with application of heat. And this is probably what happened to your
stone as well. A small price to pay for a lesson of a life time…

Hema


#4
In general remember red, white, and blue can take heat... Diamond,
Sapphire, and Ruby...That's it. 

Better to just remember diamond and corundum. Lots of other white,
red, and blue stones that won’t take much heat. But sometimes you get
surprised. In many cases, it’s not the temperatures themselves that
damage the stones, but the speed of heating or cooling that causes
fractures. That makes sense when you remember that for many stones, a
certain degree of geologic heating was involved in their formation. I
have, for example, managed to now and then heat up a garnet hotter
than should have been possible, without fracturing it. Other times,
they shatter. Same thing, occasionally, with cubic zirconia, and a
few other surprises now and then.

Nothing else can take heat. Especially in silver. 

Pretty much true. But Jane, all is not lost when you need to work on
jewelry with a heat sensative stone. While there are various products
sold (“heat sheild”) to protect heat sensative things while
soldering, they all work by being water filled gels or pastes
intended to keep the item cool. Some work OK, others only marginally.
Most suffer from the flaw of having too much structure, so heating
the metal can dry out the interface between metal and protectant,
and then the heat sinking effect, and it’s protection, stops. The
simple answer is to do without the costly products and go back to the
source. Water. If, for example, you have to size a silver ring set
with a nice heat sensative stone like turqoise, or your blue topaz,
you can simply keep the stone under water while you work. In
practice, fill an old tuna fish can or similar container with water,
and position your third hand to hold the ring halfway under water,
so the stone is submerged and the ring shank with it’s cut and fitted
seam, above the water. Now you can solder the seam. It will take a
much larger and hotter flame than you anticipate, because the silver
is sucking the heat from the joint, and the water is sucking the heat
from the silver. In short order, about the time the water in the can
is starting to boil happily, the solder will flow. But the stone
never got hotter than that boiling water, and it can take those
temperatures. Same for almost any other stone you might use. You
started with cold water, ended with boiling water and a stone at
boiling water temps. Let the stone and ring cool in air, not
quenched, since some stones (peridot, for example) might not like the
heat shock from quenching even from just 200F temps.

Alternatives to just the plain water dip are a similar container
filled with very wet sand or soldering grain. still just a can of
water in the end, but with the filler of sand or grain that can help
support the work instead of a third hand. In some cases, the can and
it’s position can be a bother. So then wrap the area needing
protection in tissue paper, hold it on with a bit of wire or thread
or string, or a locking tweezer, and dunk it in water. Be sure the
paper remains soaking wet while you work elsewhere on the ring, and
you’ll have protected the stone from undue heating. Because this
methods holds less water, it’s a bit more limited as to how long and
well it will work, but often, it’s enough.

Although, come to think of it, the synthetic spinels...ie birth
stones...can usually take heat to a degree all except the green
ones which are doublets. Must air cool these though. 

You should air cool any stone you’ve heated, including diamonds and
rubies and sapphires. quenching any of them could shatter them. Also,
if heating sapphire or ruby, be sure NOT to allow any flux or boric
acid on the stones, and don’t bathe the stones in the reducing
portions of the flame (best to keep the flame off the stones in any
case). The reason is these stones are aluminum oxide, and fluxes work
to dissolve oxides, so flux or boric acid will damage the surfaces
of the stones, while ordinary oxygen in air will not. Diamond is just
the opposite, of course. Exposed to air, it burns, leaving a frosted
white surface that needs to be repolished by a diamond cutter, so
diamonds must be very clean before any heating, and then protected
with flux or a coating of boric acid to keep oxygen off the diamond.

I have heard star sapphire and star ruby are heat sensitive too,
so I don't suggest risking heating them. 

Both of them are easy to damage, since they often have a degree of
internal strain caused by the same inclusions giving the asterism.
While heating is sometimes possible, it’s not a good idea, since
often they’ll crack, even with care. So too, can non-star rubies and
sapphires if heavily included in other ways. In fact, heavily
included diamonds are not always safe either, for the same reason.

Peter Rowe


#5
In general remember red, white, and blue can take heat... Diamond,
Sapphire, and Ruby 

Unfortunately the old red, white and blue thing is no longer
accurate. Too many stones (including diamonds) are being treated in
ways that mean that all stones should be protected from heat. If you
can’t find a way to protect a stone thoroughly while using a torch,
find someone with a laser welder to do it for you.

Daniel R. Spirer, G.G.
Daniel R. Spirer Jewelers, LLC
1780 Massachusetts Ave.
Cambrige, MA 02140
www.spirerjewelers.com


#6
The blue topaz available are irradiated stones that can change
color with application of heat. And this is probably what happened
to your stone as well. A small price to pay for a lesson of a life
time... 

The current Jewelry Artist magazine has a really interesting blurb
on that. My understanding is that the radiation causes the atoms to
shift out of their lattice structure somewhat. This causes the
colour change. When it’s heated, the heat makes them vibrate more and
they tend to slip back into their original position in the structure.
This makes the colour change back to original, and is often
accompanied by a flash of light according to the article.

Paul Anderson


#7
I have heard star sapphire and star ruby are heat sensitive too,
so I don't suggest risking heating them. 

I was lucky with mine then. I bought a synthetic star ruby a while
ago and made a chunky band ring with rails to showcase the stone. I
can’t remember what went wrong or came apart but I had to do some
soldering on the ring after I’d set the stone. I thought I’d
completely ruined it as the stone turned from a lovely dark pink
colour to a horrible blue/black colour. I was heart-broken.
Fortunately, when it cooled down, the pink colour returned to its
former glory and the star was as sharp as it had been before. You can
imagine the relief!

However, I would NOT risk it again and I’ll remember your tip,
thanks Mark.

Helen
UK
http://www.hillsgems.co.uk


#8

Citrine is generally heat treated amethyst, but heat treated before
cut I think, and don’t shock it or it’ll crack / craze. If I have to
apply heat to corundum I now always flux it well as I have "burnt"
them before (removed the polish), but that was with a very hot torch.

Robert


#9
Citrine is generally heat treated amethyst, but heat treated
before cut I think, and don't shock it or it'll crack / craze. If I
have to apply heat to corundum I now always flux it well as I have
"burnt" them before (removed the polish), but that was with a very
hot torch. 

wrong, Robert. Corundum is aluminum oxide. Fluxes dissolve metal
oxides, including aluminun oxide. A reducing soft flame will also
damage the polish on corundum if it gets too hot, but an oxidizing or
neutral flame, in air, simply will not. Experiment a bit with some
cheap flame fusion ruby to test these statements out. You’ll find I’m
correct. Put some good active white paste flux like handy flux on one
of those cheap synthetics and gently heat to a light glow (normally
much hotter than you’d like to get, but a good test for what happens
when you accidentally overheat, as can happen now and then). Let
gently cool, of course, then pickle it. You’ll find the surface to be
etched and pitted by the flux. If you do the same thing with a very
clean stone, and the flame stays oxidizing or neutral, the polish
will be just fine when the stone cools. This principal applies, by
the way, not just to active soldering fluxes, but to the plain boric
acid fire coat we often use to protect the gold from fire scale.
Boric acid will also etch the corundums if it gets too hot.

With that said, though, it’s important to also note that corundum is
not always safe to heat at all. The single most costly stone I ever
broke in the shop was a large (8 carats, I think) heart shaped ceylon
sapphire in a wonderful handmade platinum mounting. The setter had
slipped when drilling the pave plates around the bezel set sapphire,
and his drill had nicked a couple of the underwires. I thought I
could gently flow a little white gold solder into the nicks to hide
them. (I knew it wouldn’t take the temps of platinum solder, but for
small nicks, white gold solder would do the trick. Carefully fire
coated to protect the diamonds, I planned on not getting the sapphire
hot enough to damage with the flux. In fact, the torch flame never
pointed at the sapphire, and it never even got hot enough to begin to
melt the boric acid coating. But it WAS hot enough that the faint and
hard to see but fairly large included crystal, with it’s attendant
apparent fluid filled cavity, ruptured the stone. Split it in half.
I won’t tell you what that little slip cost my boss…

So be careful with all corundum, especially those you can’t afford
to replace. And please. No flux on the rubies and sapphire.

Peter
Peter Rowe


#10
In many cases, it's not the temperatures themselves that damage the
stones, but the speed of heating or cooling that causes fractures.
That makes sense when you remember that for many stones, a certain
degree of geologic heating was involved in their formation. 

This is not why some gemstones becoming damaged when heated.

What causes damage to gemstones when they heated is not sudden
temperature change, but presence of 2-phase and 3-phase inclusions.

2-phase inclusion is a cavity inside gemstone partially filled with
liquid and the rest of the volume is occupied by gas. 3-phase is the
same plus a crystal like in Colombian emeralds. Upon heating the
liquid turns to gas. Gas requires far more volume than liquid and
that shatters the stone.

Assuming that because of geological heating it could be safe to heat
some gemstones as long as it done gradually is dangerous. 2-phase
inclusions form at the later stage of hydro-thermal processes when
temperatures are relatively low. Besides, when gas becoming
entrapped, the internal pressure on cavity walls are significant, but
due to external pressure equaling internal pressure, the gas is
contained. Later on when things cool down, the gas partially
liquifies (relieving the pressure) forming a 2- phase inclusion.

When gemstone is heated, the internal pressure is reformed, but
without external pressure to counter it, the gemstone shatters.

Leonid Surpin
www.studioarete.com


#11
I have, for example, managed to now and then heat up a garnet
hotter than should have been possible, without fracturing it 

I must remember to say my daily prayers of gratitude th St Upid, who
protects us from our own idiocy…

I thought borax flux went on sapphires, too. Happily for me, I guess
I was soldering far enough from the actual stone (though not far)
because no damage is evident.

On the other hand, some years ago, I heated a glued-in citrine to
remove the epoxy. Didn’t care what happened to the stone. It came
through the direct blast of the torch on it and the silver with no
sign of change at all. Wouldn’t happen if the stone mattered, of
course! :>)

Noel